Glue-bonded multi-ply absorbent sheet and polyvinyl alcohol ply bonding adhesive

ABSTRACT

A multi-ply absorbent sheet includes a first absorbent ply of cellulosic sheet; a second absorbent ply of cellulosic sheet; and a ply bonding adhesive interposed between the first absorbent ply and the second absorbent ply, the ply-bonding adhesive thereby adhering said absorbent plies together. The ply-bonding adhesive comprises polyvinyl alcohol and nanofibrillated cellulose. In a particularly preferred embodiment the adhesive is applied as a dilute aqueous composition to tissue plies and the nanofibrillated cellulose has a Characteristic Breaking Length of 6.5 km or above.

CLAIM FOR PRIORITY

This application is a divisional application based on co-pending U.S.patent application Ser. No. 15/000,071 filed 19 Jan. 2016. U.S. patentapplication Ser. No. 15/000,071 was based on U.S. ProvisionalApplication No. 62/108,594, filed Jan. 28, 2015. The priorities of theforegoing applications are hereby claimed and their disclosuresincorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to glue-bonded, multi-plyabsorbent sheet. The present invention is directed, in part, tomulti-ply tissue wherein the plies are bonded to one another with apseudoplastic polyvinyl alcohol adhesive containing nanofibrillatedcellulose. The invention also extends to a method of making the sheet aswell as the adhesive.

BACKGROUND

Multi-ply absorbent sheet such as towel and tissue sometimesconventionally include a plurality of glue-bonded layers or plies.Adhesives employed include aqueous polyvinyl alcohol (PVOH) solutions asis disclosed in U.S. Pat. No. 3,414,459. Such solutions are relativelylow solids, less than 10% by weight PVOH and exhibit Newtonian Fluidviscosity characteristics; that is, wherein viscosity is substantiallyindependent of shear. Tissue/towel ply bonding is typically carried outin the following steps: 1) embossing one or more plies; 2) applying glueto the web on the raised emboss pattern elements; 3) bringing one ormore plies into contact with the glued surface and applying sufficientpressure to the mated web to provide enduring plybond once the glue hasdried. This process places several demands on the glue. It mustpenetrate the first web, but not too much. Enough tackiness must remainto stick to the nonglued web. The remaining glue must preferablypenetrate the nonglued web to improve the integrity of the bond. See,also, U.S. Pat. No. 5,858,554 to Neal et al., entitled Paper ProductComprising Adhesively Joined Plies which describes ply-bonded absorbentsheet provided with polyvinyl alcohol or starch adhesive compositions,note Col. 4, lines 20-55.

A paper/glue bond can be considered a fiber/polymer composite structurewith a tendency to fracture at the interface of the plies. The processand product requirements present a difficult balancing act. If the glueis too viscous, it may not penetrate either ply sufficiently. If theglue is too thin, excess glue is required to overcome the excess wickingof glue into the web. Sometimes increased marrying roll pressure is usedin an attempt to overcome the performance of the glue; however, bulk,softness and emboss quality suffer when too much pressure is used.

There is a need for a better ply bonding adhesive that overcomes thementioned deficiencies.

Nanofibrillated cellulose (NFC) or sometimes referred to asmicrofibrillated cellulose (MFC) is known in the art to be useful for avariety of purposes, including for use as a structural material in sheetand related articles. For example, in U.S. Pat. No. 6,734,335 it ismentioned that NFC is useful for use in absorbent structures. Col. 22,lines 13+. See, also, U.S. Pat. No. 7,614,110, Col. 13, lines 38+.United States Patent Application Publication No. US 2012/0219816discloses use of NFC as a layer in a multilayer paperboard structure,Abstract. See, generally, United States Patent Application PublicationNo. US 2012/0058536, ¶ [0151], which discloses NFC as a structuralmaterial. NFC is used in molded structures, as seen in United StatesPatent Application Publication No. US 2009/0308552, ¶ [0001], as well asUnited States Patent Application Publication No. US 2011/0263756,Abstract. NFC is, likewise, known for use in adhesives. JP 60250079discloses a liquid adhesive made by blending a polyvinyl acetateemulsion, sodium carboxymethyl cellulose and above 3-4% NFC based on theweight of the liquid composition. See, also, United States PatentApplication Publication No. US 2010/0285295, ¶ [0023], where NFC ismentioned as a filler for an adhesive resin; United States PatentApplication Publication No. US 2011/0052881, ¶ [0062], having similardiscussion, as well as United States Patent Application Publication No.US 2009/0042003, ¶ [0057].

SUMMARY OF INVENTION

Nanofibrillated cellulose has been found useful as a glue additive thatresults in an unexpectedly better fiber/polymer matrix by reinforcingthe interface between the plies, providing for softer products with lessglue. The NFC modifies the glue viscosity while strengthening theinterface. NFC is a shear-thinning material, so it flows more as shearis applied, and recovers viscosity as shear decreases; that is, astationary film of glue with NFC will be initially more viscous as itsits on the web surface and thin as the plies are married to enablepenetration into each paper web. The glue will thicken after marrying toretain the wet bond with less pressure. NFC has the additional benefitthat it can reinforce the interface between plies after drying.

Advantages of the invention are appreciated with references to FIGS. 1and 2. FIG. 1 is a plot of trained panel softness (arbitrary scale)versus plybond for two-ply conventional wet press (CWP) tissue with theemboss pattern shown in FIG. 4. The invention sheet had 18.7 panelsoftness when a glue containing nanofibrillated cellulose (NFC) was usedto laminate the plies with converting speeds at industrial speeds of1000, 1500 and 2000 fpm (FIG. 1). The same basesheet, laminated with thecontrol glue, was converted to 18.2 softness as described hereinafter.

FIG. 2 is a plot of Peel Test Plybond of TAD towel basesheet adheredwith glues of the invention and control glues having the samecomposition without NFC. It is appreciated from FIG. 2 that glues of theinvention provide increases in bonding strength, enabling lower glueadd-ons for providing unexpectedly softer products at comparable levelsof adhesion.

Still further features and advantages of the invention will becomeapparent from the discussion which follows.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to thedrawings wherein like numerals designate similar parts and wherein:

FIG. 1 is a plot of panel softness versus plybond for CWP tissue;

FIG. 2 is a histogram detailing Peel Test Plybond for various glueformulations applied to TAD towel;

FIG. 3 is a schematic diagram of an embossing and laminating apparatusfor preparing multi-ply absorbent sheet;

FIG. 4 is a diagram showing the pattern of raised embossments providedto the tissue basesheet by the apparatus of FIG. 3;

FIG. 5 is a diagram showing the pattern of raised embossments providedto a towel basesheet by the apparatus of FIG. 3;

FIG. 6 is a histogram showing Plybond values for various two-ply TADtowels with different glues;

FIG. 7 is a plot of trained panel softness (arbitrary scale) versusPlybond for two-ply TAD towels laminated with different glues;

FIG. 8 is a plot of trained panel softness (arbitrary scale) versus CDWet Tensile for commercial towel and towels of the invention;

FIG. 9 is a plot of viscosity versus shear rate for PVOH/NFC adhesiveand a PVOH/xanthan gum adhesive having a comparable viscosity profile;

FIG. 10 is a histogram showing Plybond for various two-ply CWP tissueproducts at various converting speeds;

FIG. 11 is a histogram showing Plybond for 2-ply structured tissueproducts at various converting speeds;

FIG. 12A is a perspective view of a three-ply product;

FIG. 12B is a schematic diagram showing an embossing and laminatingprocess for preparing 3-ply absorbent sheet;

FIG. 12C is a diagram showing a pattern for a top sheet of a 3-plyabsorbent sheet;

FIG. 12D is a diagram showing a pattern for a top sheet of another 3-plyabsorbent sheet;

FIG. 13 is a scanning electron microscope image of NFC;

FIG. 14 is a plot of Characteristic Nanofiber Viscosity versus shearrate for 4 grades of NFC at 1% solids;

FIG. 15 is a histogram detailing breaking length for 4 grades of NFCformed into handsheets or films;

FIG. 16 is a histogram detailing maximum stretch, or stretch at breakfor 4 grades of NFC, formed into handsheets or film;

FIG. 17 is a histogram detailing Specific Young's modulus for 4 gradesof NFC formed into handsheets or film;

FIGS. 18 and 19 are plots of Adhesive Viscosity versus shear rate forvarious adhesives;

FIG. 20 is a histogram showing Peel Test Plybond for various glues;

FIG. 21 is a plot showing Peel Test Plybond values for various glues asapplied to TAD towel basesheet versus PVOH concentration in weight %;and

FIG. 22 is a plot of Peel Test Plybond versus NFC concentration inweight % based on PVOH content of the aqueous adhesive; and

FIG. 23 is a plot of Glue Absorbency Rate versus PVOH content forvarious glues.

DETAILED DESCRIPTION

The invention is described in detail below in connection with theFigures for purposes of illustration, only. The invention is defined inthe appended claims. Terminology used herein is given its ordinarymeaning consistent with the exemplary definitions set forth immediatelybelow; mg refers to milligrams and m² refers to square meters, fpmrefers to feet per minute and so forth.

Adhesive Viscosity is measured at room temperature using a cone andplate geometry.

Characteristic Breaking Length of NFC material is determined by testinga strip cut from a handsheet of the subject NFC fiber as describedherein.

Characteristic Nanofiber Viscosity is measured on a 1 wt % suspension ofthe NFC in water as further described herein.

Characteristic PVOH Viscosity is measured on a 4 wt % solution of thepolyvinyl alcohol in water at a temperature of 20° C.

Relative Peel Test Plybond value refers to the ratio of the Peel TestPlybond of an NFC containing glue to that of the same glue withoutNFC×100%. The glues are tested with the same absorbent sheet by the sameequipment and procedure and have the same composition except that oneglue has no NFC. Thus, an NFC glue having 4.5% PVOH and 5% NFC having aPeel Test Plybond value of 50 g as compared with a PVOH glue of 4.5%PVOH having a Peel Test Plybond value of 20 g has a Relative Peel TestPlybond value of 50/20×100% or 250%.

A Relative Plybond value is the ratio of the Plybond of a product madewith NFC/PVOH adhesive to that of an identical product made withoutNFC×100%. That is, the products are identical in composition, processingand the same Plybond measurement is made on the product. Thus, a productmade with 5% NFC in the glue having a Plybond of 5 g as compared with anidentical product made without NFC in the glue having a Plybond value of4 g has a Relative Plybond value of 5/4×100% or 125%.

Cellulosic Sheet and Related Terminology

The term “cellulosic”, “cellulosic sheet” and the like are meant toinclude any product incorporating papermaking fiber having cellulose asa major constituent. “Papermaking fibers” include virgin pulps orrecycle (secondary) cellulosic fibers or fiber mixes comprisingcellulosic fibers. Fibers suitable for making the webs of this inventioninclude: nonwood fibers, such as cotton fibers or cotton derivatives,abaca, kenaf, sabai grass, flax, esparto grass, straw, jute hemp,bagasse, milkweed floss fibers, and pineapple leaf fibers; and woodfibers such as those obtained from deciduous and coniferous trees,including softwood fibers, such as northern and southern softwood Kraftfibers; hardwood fibers, such as eucalyptus, maple, birch, aspen, or thelike. Papermaking fibers used in connection with the invention aretypically naturally occurring pulp-derived fibers (as opposed toreconstituted fibers such as lyocell or rayon) which are liberated fromtheir source material by any one of a number of pulping processesfamiliar to one experienced in the art including sulfate, sulfite,polysulfide, soda pulping, etc.

The pulp can be bleached if desired by chemical means including the useof chlorine dioxide, oxygen, alkaline peroxide and so forth. Theproducts of the present invention may comprise a blend of conventionalfibers (whether derived from virgin pulp or recycle sources) and highcoarseness lignin-rich tubular fibers, such as bleached chemicalthermomechanical pulp (BCTMP). Pulp-derived fibers thus also includehigh yield fibers such as BCTMP as well as thermomechanical pulp (TMP),chemithermomechanical pulp (CTMP) and alkaline peroxide mechanical pulp(APMP). “Furnishes” and like terminology refers to aqueous compositionsincluding papermaking fibers, optionally wet strength resins, debondersand the like for making paper products.

Kraft softwood fiber is low yield fiber made by the well known Kraft(sulfate) pulping process from coniferous material and includes northernand southern softwood Kraft fiber, Douglas fir Kraft fiber and so forth.Kraft softwood fibers generally have a lignin content of less than 5percent by weight, a length weighted average fiber length of greaterthan 2 mm, as well as an arithmetic average fiber length of greater than0.6 mm.

Kraft hardwood fiber is made by the Kraft process from hardwood sources,i.e., eucalyptus and also has generally a lignin content of less than 5percent by weight. Kraft hardwood fibers are shorter than softwoodfibers, typically having a length weighted average fiber length of lessthan 1 mm and an arithmetic average length of less than 0.5 mm or lessthan 0.4 mm.

Recycle fiber may be added to the papermaking furnish in any amount.While any suitable recycle fiber may be used, recycle fiber withrelatively low levels of ground wood is preferred in many cases, forexample recycle fiber with less than 15% by weight lignin content, orless than 10% by weight lignin content may be preferred depending on thefurnish mixture employed and the application. Recycle fiber is in manycases 80% hardwood fiber.

“Basesheet” refers to a unitary cellulosic sheet as manufactured by apaper machine. Basesheets may be layered; however, they have a unitarystructure not readily delaminated. A “ply” of a finished product refersto basesheet incorporated into the product.

Products of the invention are made with a cellulosic fiber basesheet andhave an absorbency or SAT value as well as tensiles and densitiessuitable for tissue and towel products. Typical SAT values are greaterthan about 3 g/g in most cases. See U.S. Pat. No. 8,778,138.

“CWP” refers to absorbent products made by a conventional wet-pressprocess; that is, wet-pressing a furnish to a drying cylinder with apapermaking felt followed by creping the web from the cylinder. See U.S.Pat. No. 7,951,266, FIG. 7 thereof.

“Structured” basesheet refers to product that is wet creped (fabriccreped) from a cylinder prior to final drying. See U.S. Pat. Nos.7,850,823; 7,585,388; 7,585,389; and 7,662,257.

“TAD” refers to through-air dried absorbent products. Throughdried,creped products are disclosed in the following patents: U.S. Pat. No.3,994,771 to Morgan, Jr. et al.; U.S. Pat. No. 4,102,737 to Morton; andU.S. Pat. No. 4,529,480 to Trokhan. The processes described in thesepatents comprise, very generally, forming a web on a foraminous support,thermally pre-drying the web, applying the web to a Yankee dryer with anip defined, in part, by an impression fabric, and creping the productfrom the Yankee dryer.

The absorbent characteristics of a product can be affected by thefurnish, basis weight, strength, papermaking technology, and so forth.The sheet absorbency and converting technology for a specific productwill impact the selection of glue characteristics. CWP sheets are moreconsolidated than TAD sheets and therefore may have a lower wickingrate. Towel sheets commonly contain more softwood than tissue sheets,which may impact the pore size distribution of the web. It can beappreciated that an optimal glue formula for one product may not beoptimal for another.

A towel product is typically characterized by having predominantly (morethan 50% by weight based on fiber content) softwood fiber.

A tissue product is typically characterized by having predominantly(more than 50% by weight based on fiber content) hardwood fiber.

Laminating glue is commonly described in terms of PVOH solids. 3% PVOHglue should be understood as 3 grams of PVOH per 100 grams solution. TheNFC addition is described in most cases as a percentage of the PVOH inthe formula. Thus, “3% PVOH+5% NFC” means that the glue has 3 grams PVOHand 3*0.05=0.15 g NFC per 100 grams solution. In some cases, notablyEmbodiments 108 and following, NFC content is expressed as a weightpercentage of the aqueous composition.

Embossing and Laminating Multi-Ply Absorbent Sheet

Referring to FIG. 3, there is shown a converting apparatus 10 forembossing and plying basesheet into a multi-ply product. Apparatus 10includes a glue chamber 12 an anilox roll 14, an applicator roll 16, anembossing roll 18, a marrying roll 20 and an upper rubber roll 22 whichis softer than marrying roll 20 which is made of hard rubber.

In operation, a first basesheet 24 is fed to the nip between upper roll22 and embossing roll 18 where sheet 24 is provided with a plurality ofraised embossments having the pattern shown in FIG. 4. The pattern ofFIG. 4 provides an embossed area of raised embossments of 5.2% of thesheet area, which corresponds to the bonding area as will be appreciatedfrom the discussion which follows. Glue, including the PVOH/NFCadhesives of this invention is provided as an aqueous composition toglue chamber 12 and is picked up by anilox roll 14 and transferred toapplicator roll 16. From applicator roll 16, the glue is applied to theraised embossments of basesheet 24.

Concurrently with processing basesheet 24, a second basesheet 26 is fedthrough the nip defined by marrying roll 20 and embossing roll 18 suchthat basesheet 26 is pressed to basesheet 24, including the adhesivedisposed on the raised embossments on basesheet 24, to produce multi-plyweb 30.

Apparatus 10 was operated as described above to produce a variety ofmulti-ply tissue products, including the products described in FIG. 1.The apparatus was operated at converting speeds of 1000 fpm, 1500 fpmand 2000 fpm with basesheet of the type described in Table 1 which wasprepared by a CWP process using tissue fiber furnish (75% slush southernHW/25% slush southern SW). Details as to tissue products made from thesebasesheets appear in Table 2.

TABLE 1 Physical Properties of CWP Base Web Basis Caliper MD GM CD CDBreak Basis Weight, 8 sheet, MD CD GM MD CD T.E.A., Break T.E.A., BreakModulus Weight lb/3000 Mils/8 Tensile, Tensile, Tensile, Stretch,Stretch, mm-g/ Modulus, mm-g/ Modulus, MD Raw Wt, Description ft² shtg/3 in g/3 in g/3 in % % mm² g/% mm² g/% g/% g Basesheet 1 15.7 48.8 506232 342 29.3 7.8 1.0 22.1 0.1 28.9 17.0 1.2 Basesheet 2 15.7 46.8 555258 378 29.4 8.2 1.1 24.4 0.2 31.6 18.9 1.2

TABLE 2 Physical Properties of Converted CWP Samples Basis CaliperConverting Weight 8 Sheet Tensile Tensile Tensile speed, lb/3000 mils/MD CD GM Stretch Stretch Sample Glue fpm ft{circumflex over ( )}2 8 shtg/3 in g/3 in g/3 in MD % CD % a1 3% PVOH 1000 31.86 121.38 1,008.51489.07 701.67 28.08 8.82 1500 32.04 122.83 960.07 500.75 693.10 27.119.05 2000 32.03 120.71 935.43 468.76 661.62 27.79 9.11 a2 3% PVOH + 100032.24 120.41 999.99 496.06 703.82 28.76 9.01 5% NFC III 1500 32.33119.95 965.75 518.94 707.70 28.18 9.03 2000 32.07 120.56 956.24 487.08682.03 28.05 8.95 a3 2.5% PVOH + 1000 32.39 120.83 1,013.03 512.50720.25 29.20 8.82 5% NFC III 1500 32.06 119.91 940.26 502.39 687.0227.82 9.10 2000 32.10 120.17 948.41 486.86 679.13 28.21 9.67 Wet TensBreak Color Opacity Converting Finch Modulus Brtness MacBeth MacBethspeed, CD GM MacBeth b*-UV C Opacity Sample Glue fpm g/3 in g/% UV-C %Unitless Units a1 3% PVOH 1000 64.27 44.53 83.12 6.12 72.99 1500 63.8944.36 83.44 6.06 73.62 2000 59.56 41.20 83.51 5.98 73.09 a2 3% PVOH +1000 63.08 43.55 83.29 6.15 73.89 5% NFC III 1500 64.46 43.93 83.39 6.0773.70 2000 62.14 43.20 83.38 6.06 73.71 a3 2.5% PVOH + 1000 65.13 44.7983.60 6.00 73.45 5% NFC III 1500 63.56 42.70 83.45 6.04 73.76 2000 60.4541.12 83.65 5.98 73.73 Roll Color Color Converting TMI Roll CompressBreak Break MacBeth MacBeth speed, Plybond Diameter Value ModulusModulus a*-UV L*-UV Sample Glue fpm g in % MD g/% CD g/% CUnitlessCUnitless a1 3% PVOH 1000 6.35 4.50 27.24 35.91 55.29 −1.23 96.40 15005.65 4.54 29.13 35.53 55.43 −1.25 96.50 2000 3.58 4.53 27.20 33.31 51.01−1.22 96.50 a2 3% PVOH + 1000 4.91 4.57 28.47 34.65 54.78 −1.24 96.50 5%NFC III 1500 4.01 4.57 28.52 33.76 57.19 −1.25 96.50 2000 4.01 4.5728.87 34.26 54.50 −1.23 96.49 a3 2.5% PVOH + 1000 3.27 4.55 28.33 34.3658.43 −1.24 96.55 5% NFC III 1500 3.44 4.57 29.93 33.71 54.14 −1.2596.50 2000 3.21 4.58 29.55 33.33 50.78 −1.21 96.56 T.E.A. T.E.A.Converting MD CD Basis Roll speed, mm-g/ mm-g/ Weight Comp Sample Gluefpm mm{circumflex over ( )}2 mm{circumflex over ( )}2 Raw Wtg inSoftness a1 3% PVOH 1000 1.98 0.32 2.41 3.28 18.1 1500 1.85 0.34 2.423.22 18.2 2000 1.86 0.32 2.42 3.30 18.2 a2 3% PVOH + 1000 2.01 0.34 2.443.27 18.1 5% NFC III 1500 1.91 0.36 2.44 3.27 18.2 2000 1.88 0.33 2.423.25 18.2 a3 2.5% PVOH + 1000 2.03 0.34 2.45 3.26 18.6 5% NFC III 15001.85 0.35 2.42 3.20 18.7 2000 1.88 0.36 2.43 3.23 18.7

A series of towel products were prepared using the apparatus of FIG. 3using a towel basesheet (100% softwood Kraft fiber) prepared by a TADprocess. The basesheet had the properties indicated in Table 3. Thefinished product was provided with the pattern of raised embossmentsshown in FIG. 5 and plied with the glue formulations shown in Table 4,which also provides property data on the two-ply towel.

TABLE 3 Physical Properties of TAD Towel Basesheet Basis Caliper WetTens T.E.A. Break T.E.A. Break Break Weight 8 Sheet Tensile TensileTensile Stretch Stretch Finch MD Modulus CD Modulus Modulus lb/3000mils/ MD CD GM MD CD Cured CD mm · g/ GM mm · g/ CD MD ft{circumflexover ( )}2 8 sht g/3 in g/3 in g/3 in % % g/3 in mm{circumflex over( )}2 g/% mm{circumflex over ( )}2 g/% g/% 15.72 100.90 1242 1196 121813.6 7.1 342.32 1.133 123.23 0.569 167.71 90.57 15.40 101.75 1375 12401305 14.6 7.7 342.89 1.351 123.44 0.596 158.92 95.90

TABLE 4 Physical Properties of Converted TAD Paper Towels Basis CaliperTensile Wet Tens Tensile Weight 8 Sheet Tensile Stretch Tensile StretchTensile Dry Finch Wet/Dry SAT SAT lb/3000 mils/ MD MD CD CD GM RatioCured CD CD Capacity Rate Actual Glue Sample ft{circumflex over ( )}2 8sht g/3 in % g/3 in % g/3 in Unitless g/3 in Unitles g/m{circumflex over( )}2 g/s{circumflex over ( )}0.5 5% PVOH 31.2 214.2 2248 15.3 1951 8.02094 1.15 527 0.27 540 0.32 4.6% PVOH + 5% NFC 31.2 213.4 2336 15.4 19948.2 2157 1.17 512 0.26 549 0.32 4.4% PVOH + 5% NFC 31.1 213.9 2241 15.02027 8.1 2131 1.11 532 0.26 537 0.30 4% PVOH + 15% NFC 31.2 215.0 229015.3 1964 8.1 2120 1.17 514 0.26 547 0.32 3.6% PVOH + 15% NFC 31.4 214.82262 15.0 1998 8.3 2126 1.13 525 0.26 535 0.32 4.2% PVOH 30.7 209.9 239214.7 2019 8.0 2197 1.18 535 0.27 538 0.28 4.2% PVOH + 10% NFC 30.8 211.82186 14.6 1918 8.1 2047 1.14 517 0.27 546 0.32 3.9% PVOH 31.3 213.1 223314.6 1931 7.8 2076 1.16 521 0.27 536 0.32 3.8% PVOH + 15% NFC 30.9 212.32206 15.1 1866 7.9 2029 1.18 511 0.27 558 0.31 3.8% PVOH + 10% NFC 30.7211.9 2169 14.9 1917 8.1 2039 1.13 502 0.26 554 0.31 Break Break BreakT.E.A. T.E.A. Roll SAT Modulus Modulus Modulus MD CD Roll Compress RollTime MD CD GM mm · g/ mm · g/ Diameter Value Comp Actual Glue Sample sg/% g/% g/% mm{circumflex over ( )}2 mm{circumflex over ( )}2 in % inSoftness 5% PVOH 29.6 147 244 189 2.1 1.1 4.58 9.2 4.16 7.7 4.6% PVOH +5% NFC 27.2 152 240 191 2.2 1.1 4.58 9.3 4.15 8 4.4% PVOH + 5% NFC 28.3150 254 195 2.1 1.1 4.59 9.7 4.15 7.9 4% PVOH + 15% NFC 26.2 150 244 1912.2 1.1 4.60 9.8 4.15 7.6 3.6% PVOH + 15% NFC 28.6 153 241 192 2.1 1.14.60 10.1 4.14 7.8 4.2% PVOH 28.6 163 253 203 2.2 1.1 4.57 11.4 4.05 7.84.2% PVOH + 10% NFC 26.8 150 236 188 2.0 1.0 4.57 10.3 4.10 7.8 3.9%PVOH 25.7 154 249 196 2.0 1.0 4.60 10.7 4.11 7.6 3.8% PVOH + 15% NFC24.8 146 236 186 2.0 1.0 4.58 10.3 4.11 7.7 3.8% PVOH + 10% NFC 25.1 147238 187 2.0 1.1 4.59 10.2 4.12 7.6

It is appreciated from FIG. 6 that the NFC containing glues of theinvention provided unexpected results in Plybond values to PVOH glues,making it possible to use less glue for a given Plybond. This latterfeature is believed to provide better softness as is seen in FIGS. 7 and8. In FIG. 7, it is seen that 4.6% and 4.4% POH glues with NFC providebetter Plybond and better softness than the 5% PVOH control. In FIG. 8,it is seen the invention products have low CD Tensile values and highersoftness values than corresponding conventional products. In general,Wet CD Tensile is believed inversely related to softness which isconsistent with results seen in FIG. 8.

Apparatus 10 was also used to compare NFC containing PVOH adhesives withsimilar PVOH adhesives containing xanthan gums, described below.

Comparison with Xanthan Gum Glue Modifier

For purposes of discerning whether the properties imparted by theinventive adhesive to multi-ply sheet were due to viscosity modificationof PVOH alone or whether the NFC imparted additional benefits, PVOHadhesives with NFC and with Xanthan gum instead of NFC, were prepared asdescribed above. These adhesives had the composition and viscosityprofiles shown in FIG. 9.

These adhesives were used to produce two-ply, glue-bonded tissue asdescribed generally in connection with the products described in Table 2with two-ply CWP embossed tissue. Plybond results appear in FIG. 10.

The two-ply CWP bath tissue produced demonstrated that:

-   -   NFC provides a plybond reinforcement effect for two-ply CWP    -   The plybond improved by 77% and 25% at converting speed of 1500        fpm and 2000 fpm, respectively, with the addition of 2% NFC in        2.5% PVOH.    -   The improvement of plybond by NFC reinforced glue was not only        due to viscosity.

These adhesives were also used to produce two-ply, glue-bonded tissue asdescribed generally in connection with the products described in Table 5with structured (fabric creped), embossed tissue. Plybond results appearin FIG. 11.

TABLE 5 Structured Two-Ply Tissue Properties two-ply Basis Caliper WetTens Break structured Bath Weight 8 Sheet Tensile Tensile TensileStretch Stretch Finch Modulus TMI Tissue lb/3000 mils/ MD CD GM MD CD CDGM Plybond Description Sample ft{circumflex over ( )}2 8 sht g/3 in g/3in g/3 in % % g/3 in g/% g Structured 43 26.7 124.1 963 630 779 17.5 7.879.1 66.9 2.5 Structured 44 26.9 125.5 931 622 760 17.2 7.9 76.6 65.52.1 Structured 45 26.7 125.5 938 599 749 17.0 7.7 79.1 65.5 1.8Structured 46 27.0 125.7 940 597 748 16.4 7.9 77.1 66.3 1.0 Structured47 26.7 125.3 886 577 714 15.9 7.6 74.9 65.7 0.8 Structured 48 27.1126.0 891 605 734 15.3 7.4 77.4 69.5 0.7 Structured 49 26.8 125.3 922603 745 15.3 7.4 77.6 70.3 1.6 Structured 52 27.5 124.3 967 657 796 17.17.5 81.7 70.8 1.8 Structured 53 27.4 124.7 954 645 784 17.9 7.5 79.168.1 1.5 Structured 55 27.1 124.7 931 615 756 17.5 7.5 77.5 65.9 1.3Structured 56 27.1 125.0 947 612 761 17.2 7.5 76.6 67.5 1.1 Structured57 27.2 123.9 934 585 739 17.6 7.3 74.5 66.1 0.9 two-ply Roll BreakBreak T.E.A. T.E.A. structured Bath Roll Compress Modulus Modulus MD CDRoll Total Tissue Diameter Value MD CD mm-g/ mm-g/ Comp solids,Description in % g/% g/% mm{circumflex over ( )}2 mm{circumflex over( )}2 in Softness % Structured 4.3 18.3 55.0 81.4 1.2 0.3 3.5 Structured4.3 19.8 53.9 79.6 1.1 0.3 3.4 19.10 3.00 Structured 4.3 21.4 54.9 78.31.1 0.3 3.4 Structured 4.3 21.3 57.1 77.1 1.1 0.3 3.4 Structured 4.322.3 56.0 77.3 1.0 0.3 3.3 19.10 2.50 Structured 4.2 22.3 58.5 82.5 1.00.3 3.3 Structured 4.3 23.1 60.5 81.8 1.0 0.3 3.3 19.30 2.00 Structured4.2 20.6 57.4 87.4 1.2 0.3 3.4 Structured 4.2 23.5 53.4 87.0 1.2 0.3 3.219.10 2.55 Structured 4.3 19.7 53.8 80.8 1.2 0.3 3.4 Structured 4.3 22.756.1 81.2 1.2 0.3 3.3 19.30 2.51 Structured 4.3 22.3 54.0 80.9 1.2 0.33.3

The structured bath tissue demonstrated that:

-   -   two-ply structured bath tissue had significantly lower plybond        by using the same glue and same converting conditions as two-ply        CWP.    -   NFC shows plybond reinforcement effect for two-ply structured        bath tissue. The plybond improved by 80% and 88% at converting        speed of 1000 fpm and 1500 fpm, respectively, with the addition        of 2% NFC in 2.5% PVOH.    -   The improvement of plybond by NFC reinforced glue was not only        due to viscosity.        Three-Ply Products

In some preferred embodiments, the present invention relates tothree-ply products such as three-ply tissue products as shown in FIG.12A. A three-ply product 35 includes a first outer ply 38, a central ply40 and a second outer ply 42. The plies are adhered together by PVOH/NFCadhesive securing plies together at their interfaces indicated at 44,46. Three-ply products may be made by successive lamination of the pliesor by way of simultaneous lamination as is known in the art. Towelproducts may likewise be produced as three-ply absorbent structures, ifso desired.

One preferred method of preparing 3-ply absorbent sheet is illustratedin connection with FIG. 12B, wherein there is shown a convertingapparatus 110 for embossing and plying basesheet into a multi-plyproduct. Apparatus 110 includes a glue chamber 112 an anilox roll 114,an applicator roll 116, an embossing roll 118, a marrying roll 120 andan upper rubber roll 122 which is softer than marrying roll 120 which ismade of hard rubber. A micro-embossing nip 145 including amicro-embossing roll 147 and a rubber roll 149 is provided for embossinga bottom sheet, as is noted below.

In operation, a top ply basesheet 138 and a middle ply basesheet 140 arefed to the nip between upper roll 122 and embossing roll 118 where thetop ply (and to a lesser extent, ply 140) are provided with an embosspattern. NFC/PVOH glue is provided as an aqueous composition to gluechamber 112, is picked up by anilox roll 114 and transferred toapplicator roll 116. From applicator roll 116 the glue is applied tosheet 140.

Concurrently with processing layers 140, 138, a bottom ply basesheet 142is fed to micro-embossing nip 145 where it is micro-embossed. Sheet 142is advanced to the nip defined by marrying roll 120 and embossing roll118 such that the layers are pressed together to produce 3-ply product135.

Using the procedures and materials generally described above, 3-plytissue products were prepared by micro embossing the bottom ply andapplying the ply bonding adhesive on the middle layer followed bypressing the middle and bottom plies together, as shown and described inconnection with FIG. 12B. The development of the target plybond betweenthe top and middle layer was due to the adhesive wicking through tomiddle layer facilitated by marrying roll pressing. Although PVOH/NFCglue had less and slower penetration into the sheet, due to the highlyefficient reinforcement property of NFC, even a little PVOH/NFC gluemight achieve the target plybond (2.2 g) between the top and middlelayer. For a top sheet emboss pattern bordered by compressed lines as isseen in FIG. 12C, results appear in Table 6. The NFC glue resulted in a0.2 sensory softness boost at the same GM tensiles and the same finishedproduct ply bond of 2.2 g, when added to the PVOH glue when it was 4.1%solids. There was a 0.1 sensory softness boost when added to the PVOHglue when it was at 3.5% solids.

TABLE 6 3-Ply Softness, Plybond NFC glue 1 NFC glue 2 Control 4.1%PVOH + 3.5% PVOH + glue 5% NFC (4.3% 5% NFC 3.7% 5% PVOH total solids)total solids) Softness 19.6 19.8 19.7 Geometric mean 594 598 629tensile, g/3″ TMI plybond, g 2.2 2.2 2.2

Using a slightly different top sheet emboss pattern, bordered by dottedlines as is seen in FIG. 12D, the NFC boosted glue yielded the samesensory softness as ply bond glue. Results appear in Table 7. Note thatthe plybond was significantly higher for the NFC prototype. Due to theincreased geometric mean tensile of the finished product listed in Table7, and possibly the differences in the emboss patterns, the overallsensory softness for both of these prototypes was significantly lowerthan for the sensory softness for the prototypes made in Table 6.

TABLE 7 3-Ply Softness, Plybond Control PVOH 5% PVOH glue glue (5% with5% NFC total solids) (5.25% total solids) Softness 19.2 19.2 Geometricmean 758 789 tensile, g/3″ TMI plybond, g 1.6 6.4

Further details concerning materials, adhesive formulation and testingare described below.

Materials, Adhesive Formulation and Sample Testing

Dry tensile strengths, stretch, ratios thereof, modulus, break modulus,stress and strain are measured with a standard Instron test device orother suitable elongation tensile tester which may be configured invarious ways, typically using 3 or 1 inch wide strips of material,suitably conditioned in an atmosphere of 23°±1° C. (73.4°±1° F.) at 50%relative humidity for 2 hours. This conditioning method is preferablyemployed for all specimens testing. The tensile test is typically run ata crosshead speed of 2 in/min. Tensile strength is sometimes referred tosimply as “tensile” and is reported herein for NFC as breaking length(km), which is the tensile in kg/m divided by the basis weight of thesample in g/m². See U.S. Pat. No. 8,409,404 for additional measurementsand details.

The term “Characteristic Breaking Length” when referring to NFC refersto the breaking length of a handsheet or film made from 100% of the NFC.The handsheet (50-70 g/m²) is made by using vacuum filtration and asuitable membrane as is described in more detail hereinafter followed byrestrained air drying

The modulus of a specimen (also referred to as stiffness modulus ortensile modulus) is determined by the procedure for measuring tensilestrength described above, using a sample with a length of 1 inch andwidth of 15 mm (0.59 in), and the modulus recorded is the chord slope ofthe load/elongation curve measured over the range of 0-50 grams load.The specific modulus is the modulus divided by density.

Polyvinyl Alcohol and Characteristic PVOH Viscosity

Characteristic PVOH Viscosity is measured at 4 wt % solution of thepolyvinyl alcohol in water at a temperature of 20° C. Viscosity isexpressed in centipoises unless otherwise indicated, abbreviated cps orcP.

Polyvinyl alcohols for use in connection with the present inventioninclude those obtainable from Sekisui Specialty Chemicals, Houston, Tex.as well as other suppliers and distributors. Commercial polyvinylalcohol resins are produced by saponifying polyvinyl acetate and includesignificant levels of vinyl acetate repeat units. The degree ofhydrolysis (mol %) indicates the mol % alcohol repeat units in thepolyvinyl alcohol, with the remainder being in acetate form. A partiallyhydrolyzed polyvinyl alcohol may be used and dissolved in water that isfrom about 70 mole percent to about 90 mole percent hydrolyzed, such asfrom about 84 mole percent to about 89 mole percent hydrolyzed.Partially hydrolyzed polyvinyl alcohols more rapidly dissolve; however,polyvinyl alcohols that are hydrolyzed to a greater extent may be used.For instance, polyvinyl alcohols may also be used in the process thathas a percent hydrolysis (mole %) of greater than 90%. In some cases,the polyvinyl alcohol may be from about 91% to about 99.31% hydrolyzed.The molecular weight of the polyvinyl alcohol used can also vary. Arelatively low molecular weight polyvinyl alcohol may be used. Forinstance, the polyvinyl alcohol may have a viscosity at 4% solids and at20° C. of less than about 10 cps. For instance, the viscosity of thepolyvinyl alcohol at 4% solids and 20° C. can be from about 3.5 cps toabout 4.5 cps. In other embodiments, however, higher molecular weightpolyvinyl alcohols can be used that have a viscosity at 4% solids and at20° C. of greater than about 5 cps, such as up to about 75 cps.Generally, polyvinyl alcohol or PVOH resins consist mostly of hydrolyzedpolyvinyl acetate repeat units (more than 50 mole %), but may includemonomers other than polyvinyl acetate in amounts up to about 10 mole %or so in typical commercial resins. Suitable co-monomers include vinylco-monomers in general and especially those with carboxylate orsulfonate functionality as is seen in U.S. Pat. No. 7,642,226. Typicalcommercial polyvinyl alcohols are listed in Table 8 below.

TABLE 8 Commercial Polyvinyl Alcohol for Adhesive % Viscosity,Volatiles, % Ash, % Grade Hydrolysis, cps¹ pH Max. Max.³ SuperHydrolyzed Selvol 125 99.3+ 28-32 5.5-7.5 5 1.2 Selvol 165 99.3+ 62-725.5-7.5 5 1.2 Fully Hydrolyzed Selvol 103 98.0-98.8 3.5-4.5 5.0-7.0 51.2 Selvol 107 98.0-98.8 5.5-6.6 5.0-7.0 5 1.2 Selvol 310 98.0-98.8 9.0-11.0 5.0-7.0 5 1.2 Selvol 325 98.0-98.8 28.0-32.0 5.0-7.0 5 1.2Selvol 350 98.0-98.8 62-72 5.0-7.0 5 1.2 Intermediate Hydrolyzed Selvol418 91.0-93.0 14.5-19.5 4.5-7.0 5 0.9 Selvol 425 95.5-96.5 27-31 4.5-6.55 0.9 Partially Hydrolyzed Selvol 502 87.0-89.0 3.0-3.7 4.5-6.5 5 0.9Selvol 203 87.0-89.0 3.5-4.5 4.5-6.5 5 0.9 Selvol 205 87.0-89.0 5.2-6.24.5-6.5 5 0.7 Selvol 513 86.0-89.0 13-15 4.5-6.5 5 0.7 Selvol 52387.0-89.0 23-27 4.0-6.0 5 0.5 Selvol 540 87.0-89.0 45-55 4.0-6.0 5 0.5¹4% aqueous solution, 20° C.Commercial adhesive formulations containing PVOH are available from avariety of sources including H. B. fuller of Minnesota. Suchcompositions may contain optional additives if so desired. See U.S. Pat.No. 7,201,815.Nanofibrillated Cellulose

NFC is commonly produced by mechanically disintegrating wood pulp, suchas hardwood or softwood Kraft pulp which can include chemical pre- orpost-treatments. The pulp used may be pre-processed enzymatically orchemically, for example, to reduce the quantity of hemicellulose.Furthermore, the cellulose fibers may be chemically modified, whereinthe cellulose molecules contain functional groups other than in theoriginal cellulose. Such groups include, among others, carboxymethyl(CMC), aldehyde and/or carboxyl groups (cellulose obtained by N-oxylmediated oxidation, for example “TEMPO”), or quaternary ammonium(cationic cellulose).

Generally, a high shear zone is formed during disintegration todelaminate multilayer cell walls of wood fibers and separate fibrilswhile minimizing cutting and entangling. This process is used to isolatehigh aspect ratio, semi-crystalline cellulose fibrils with robustmechanical properties from the wood furnish. Nanofibrils are typicallyon the order of 4-20 nm wide and 500-2000 nm long. They possess goodaxial tensile strength due to inter- and intra-molecular hydrogenbonding among highly oriented cellulose molecules. Various processessuitable for making NFC are described in the following references:United States Patent Application Publication No. US 2011/0277947,entitled “Cellulose Nanofilaments and Method to Produce Same”, of Hua etal.; United States Patent Application Publication No. US 2014/0083634,entitled “Method and an Apparatus for Producing Nanocellulose”, ofBjoerkqvist et al.; and United States Patent Application Publication No.US 2014/0284407, entitled “A Method for Producing NanofibrillarCellulose”, of Tamper et al.

The fiber morphology influences the amount of energy required todisintegrate it into NFC. Delamination can be facilitated by weakeningfiber cell walls or decreasing the strength of fiber-to-fiber bondsthrough enzymatic or oxidative pretreatments as noted above.Pretreatments can be targeted to certain regions of the fiber or cause ageneral weakening effect. For example, cellulase enzymes degrade theamorphous portion of the fiber, whereas the TEMPO oxidation weakens theentire surface of the fiber by decreasing the degree of polymerizationof cellulose. The TEMPO pretreatment weakens the fiber indiscriminatelyby converting primary hydroxyl groups of polysaccharides to carboxylgroups. The same techniques can also be used after mechanicalfibrillation to achieve a desired quality of NFC. The choice and extentof pretreatment, as well as the morphology of the starting material,will influence the morphology of the nanofibrillated cellulose produced.For example, pulps that undergo extensive enzymatic hydrolysis beforedisintegration tend to be more uniform in size with a higher degree ofcrystallinity. With a lower fraction of amorphous cellulose, thesefibers look more like cellulose nanocrystals and have a lower specificsurface area. Mechanical disintegration with a microgrinder willincrease the surface area of the fibrils and cause more branching. Forglue reinforcement applications, this is a desired outcome as greatersurface area will increase the amount of interfacial bonding with thematrix glue, PVOH.

Further details concerning making NFC or MFC with peroxide or ozone areseen in U.S. Pat. No. 7,700,764 to Heijnesson-Hultén, entitled Method ofPreparing Microfibrillar Polysaccharide (Akzo Nobel N.V.); United StatesPatent Application Publication No. US 2015/0167243 of Bilodeau et al.,entitled Energy Efficient Process for Preparing Nanocellulose Fibers(University of Main System Board of Trustees); and U.S. Pat. No.8,747,612 to Heiskanen et al., entitled Process for the Production ofMicrofibrillated Cellulose in an Extruder and Microfibrillated CelluloseProduced According to the Process (Stora Enso OYJ). Discussion relatingto making NFC or MFC with N-oxyl compounds is seen in U.S. Pat. No.8,992,728 to Isogai et al., entitled Cellulose Nanofiber, ProductionMethod of Same and Cellulose Nanofiber Dispersion (University of Tokyo);U.S. Pat. No. 8,377,563 to Miyawaki et al., entitled PapermakingAdditive and Paper Containing the Same (Nippon Paper Industries Co.,Ltd.); and U.S. Pat. No. 8,287,692 to Miyawaki et al., entitledProcesses for Producing Cellulose Nanofibers (Nippon Paper IndustriesCo., Ltd.) which discloses a process for making nanofibers using N-oxylcompounds (TEMPO). References for making NFC or MFC with enzymes includeU.S. Pat. No. 8,778,134 to Vehvilainen et al., entitled Process forProducing Microfibrillated Cellulose (Stora Enso OYJ); U.S. Pat. No.8,728,273 to Heiskanen et al., entitled Process for the Production of aComposition Comprising Fibrillated Cellulose and a Composition (StoraEnso OYJ); U.S. Pat. No. 8,647,468 to Heiskanen et al., entitled Processfor Producing Microfibrillated Cellulose (Stora Enso OYJ) which proposestwo enzymatic treatments of the pulp used to make microfibers; and U.S.Pat. No. 8,546,558 to Ankerfors et al., entitled Method for theManufacture of Microfibrillated Cellulose (STFI-Packforsk AB) which alsorelates to the use of an enzyme treatment.

NFC may be obtained through the University of Maine; see “The Universityof Maine—The Process Development Center—Nanofiber R & D,” [Online].Available: http://umaine.edu/pdc/nanofiber-r-d/. [Accessed 24 Nov.2014]. This source is referred to as NFC I in the text and figures. NFCmay also be obtained from Centre Technique du Papier in Grenoble,France. This source will be referred to as NFC II in the text andFigures. NFC may also be obtained from Paperlogic, operator of the firstUS commercial nanocellulose plant at the former Southworth Paper and nowPaperlogic mill in Turners Falls, Mass. This source is referred to asNFC PL.

Table 9, below, shows energy input data and fiber length data for atypical disintegration process for making NFC, wherein the pulp employedwas southern hardwood Kraft fines and the pulp was ground in a diskgrinder at essentially zero gap. It is seen in Table 9 that the fiberlength decreases substantially and the fines increase sharply as thepulp is ground. The NFC formed by this process is shown in the electronmicroscope image of FIG. 13. This source of NFC will be referred to asNFC III in the text and figures. While hardwood fines are generallyregarded as an undesirable pulp fraction, they may be suitable formaking NFC suitable for use in adhesives with the advantage that NFCproduced from this material requires less energy input than NFC producedfrom Kraft pulp generally, which usually has a fines content of lessthan 50% by MorFi® fiber analysis, discussed below. Thus, the adhesivesof the invention advantageously employ NFC made from pulp having greaterthan 50% fines (% files (Lw) as discussed below.

TABLE 9 Calculated energy input and fiber length for nanofibrillatedcellulose made from Southern Hardwood Fines Gross Net energy Grossenergy Power Cumulative Energy/ cumulative Time (watts) Net Gross (KW-time (KW- L_(w) Fines (min) 264 KW KW hr/mt) increment hr/mt) (mm) (%length) 0 528 0.264 0.0 0.0 0.725 76.5 15 432 0.168 0.432 140.7 361.8361.8 0.657 77.7 30 432 0.168 0.432 282.1 363.6 725.4 0.589 80.1 45 4320.168 0.432 424.2 365.5 1090.9 0.528 83.7 60 408 0.144 0.408 546.7 346.91437.9 0.46 87 90 408 0.144 0.408 792.9 697.4 2135.3 0.374 93 105 4080.144 0.408 916.6 350.5 2485.8 0.36 94

The fiber length data in Table 9 was measured with a MorFi® fiberanalyzer (MFA) which calculates fiber length as:

$L_{w} = \frac{\Sigma\; n_{i}L_{i}^{2}}{\Sigma\; n_{i}L_{i}}$

i=1, 2 . . . N categories (bins)

n_(i)=fiber count in the i^(th) category/bin

L_(i)=contour length−histogram class center length in the i^(th)category/bin

The smallest “fine” particle the MFA records include is about 5 μm andit measures fibers up to about 10 mm in length in the Lw calculation.While the analyzer excludes nanofibrils, the data nevertheless providesa characterization of the fibrillation process in terms of lengthreduction and fines increase as the cellulose pulp is nanofibrillated.

The MFA calculates the length weighted fines content by summing up thelength of all the fines, Lfines, (i.e. 10 μm<fiber length<200 μm)divided by the length of all fibers, LT:

${\%\mspace{14mu}{F\left( L_{w} \right)}} = \frac{\Sigma\; L_{fines}}{L_{T}}$

For present purposes, NFC is characterized by viscosity profiles andbreaking length as is discussed below.

Characteristic Nanofiber Viscosity and Adhesive Viscosity

Characteristic Nanofiber Viscosity is measured on a 1 wt % suspension ofthe subject NFC in water.

Viscosity of the glues and NFC suspensions is measured at roomtemperature, using a TA instruments Discovery Hybrid Rheometer (DHR) 2.A cone and plate geometry was used for analysis. A few drops of samplewere placed on a flat metal peltier plate and the cone spindle, whichhas a 60 mm diameter and 2° angle, was brought down to make contact withthe sample to initiate the spreading action. The sample that flowed outof the circumference of the cone spindle was trimmed. The experimentalconditions were as follows: flow logarithmic sweep, shear rate 0.5-2000Hz at room temperature. Trim and geometric gap was 54 microns. Roomtemperature means ambient temperature between 23° C. and 29° C.,typically. If a specific value is required, 25° C. is used.

Viscosity Analysis of NFC

NFC suspensions were prepared to obtain 1% consistency. The suspensionswere then characterized for their viscosity profiles using the testmethod and apparatus described above. Results appear in Table 10.

TABLE 10 NFC Viscosity Profiles shear rate, NFC I NFC II NFC III NFC Pl1/s Viscosity,cP Viscosity, cP Viscosity, cP Viscosity, cP 0.5 523000989 9190 47567.1 0.8 366000 650 5940 30257 1.3 237000 387 4360 20858.72.0 144000 229 2910 18659.4 3.2 108000 144 2000 20986.7 5.0 80400 1071320 33391.9 7.9 93300 80.9 843 50741.6 12.6 54100 61.2 548 51552.9 19.972000 50.3 579 53049.5 31.5 53200 53.8 1400 46991.5 50.0 21900 42 130017077.7 79.2 14100 23 1160 9200.18 126.0 5670 15.1 983 9716.41 199.02640 11.4 683 5740.54 315.0 1190 9.08 473 3052.84 500.0 553 7.61 3031381.11 792.0 234 6.65 198 673.671 1260.0 100 6.15 132 307.663 1990.045.8 6.13 75.4 123.97 2000 30.8 6.03 79.5 111.168

The data from Table 10 is shown graphically in FIG. 14. It isappreciated from FIG. 14 that NFC properties vary depending upon thedegree of fibrillation, especially at low shear. At higher shear rates,viscosity values converge.

NFC Breaking Length, Stretch and Modulus

100% NFC films or handsheets were formed by vacuum filtration usingnylon membrane with 0.45 μm pore size utilizing the NFC I, NFC II, NFCIII and NFC Pl materials. Fully restrained drying of NFC films wasconducted by attachment of one side of the film to a metal plate and theother side was pressed by a customized perforated ring with a piece ofheavy metal on top. The diameter of dried NFC films was 1.5 in. Eachfilm was cut into a 15 mm×1 in strip for tensile testing which providedthe information to calculate the breaking length, maximum stretch atbreak, and Specific Young's modulus. Results appear in Table 11, as wellas in FIGS. 15, 16 and 17 for NFC I, II, III and PL.

TABLE 11 NFC Properties and Sheet Basis Weight Specific Breaking MaxYoung's Basis length, stretch, modulus, Weight, Sample km % Mpa/g.cm³g/m² NFC I 6.9 7.5 2194 56 NFC II 5.9 4.6 2095 59 NFC III 5.0 7.0 115669 NFC Pl 6.3 11.4 1416 62Glue Formulation

Glue was formulated from commercial polyvinyl alcohol (PVOH) adhesiveand NFC by diluting a commercially available 8% solids by weight aqueousPVOH adhesive and thoroughly mixing with NFC as detailed in Table 12,wherein it is seen Conventional PVOH glue was diluted to 4-6% solidcontent from commercial PVOH plybond water-based adhesive (WB2746, H.B.Fuller, 8% solids). Two types of NFC were employed in the formulationsof Table 12: NFC I, a relatively fine grade in an aqueous dispersion,3.28% by weight solids; NFC II, a somewhat coarser grade in an aqueousdispersion, 1.92% solids were mixed with the commercial PVOH to prepareNFC reinforced PVOH glues having the composition shown in Table 12.

TABLE 12 Preparation of Glue PVOH 8% 3.28% 1.92% Glue Solids, % PVOH,NFC I, NFC II, Water, Total, # Sample (w/w) g g g g g 1 PVOH 4 150150.00 300.00 2 4.5 170 132.22 302.22 3 5 190 114.00 304.00 4 5.5 21095.45 305.45 5 6 225 75.00 300.00 6 PVOH + 4 150 18.29 131.71 300.00 75% NFC I 4.5 170 20.73 111.49 302.22 8 5 190 23.17 90.83 304.00 9 5.5210 25.61 69.84 305.45 10 6 225 27.44 47.56 300.00 11 PVOH + 4 150 31.25118.75 300.00 12 5% NFC II 4.5 170 35.42 96.81 302.22 13 5 190 39.5874.42 304.00 14 5.5 210 43.75 51.70 305.45 15 6 225 46.88 28.13 300.00

The above and additional glues with different levels of PVOH and NFCwere tested for their viscosity with respect to shear rate using theprocedure noted above. The viscosity of each glue represented ascentiPoise vs. shear rate ({dot over (γ)}, which is proportional torotor speed and inversely related to gap) is shown in FIGS. 18 and 19.All the PVOH glues without NFC were typical newtonian fluids in whichviscosity stays the same regardless of shear rate in the range of0.5-2000 s⁻¹. Viscosity of 4.5% PVOH was over three times the viscosityof 3% PVOH. All the glues that contain 5% NFC based on the dry weight ofPVOH displayed a shear thinning property. For the NFC reinforced glues,3% PVOH+5% NFC and 4.5% PVOH+5% NFC, the incorporation of NFCsignificantly increased the viscosity of the glue and the degree ofincrease depends on the shear rate. Two glue samples, 3% PVOH and 2.5%PVOH+5% NFC, had very similar viscosity curves. Therefore, it is likelythat a similar volume of glue will be applied on base web when usingthese two types of glue. However, 2.5% PVOH+5% NFC provides a benefit interms of softness since less total PVOH is used as is seen in FIG. 1.

FIGS. 18, 19 likewise show that standard PVOH glue is converted from aNewtonian fluid to a pseudoplastic (shear-thinning) fluid by addition ofa small quantity of NFC. Low-shear viscosity is also significantlyincreased. Glue containing 2.5% PVOH with NFC has a viscosity in asimilar range as 3% PVOH. If the fluid dynamics of each glue results inthe transfer of a similar liquid volume, it is reasonable to assume thatthe NFC glue supplied about 20% less PVOH (2.5/3). Softness is improveddue to the smaller amount of glue being less detectable to touch. Theglue/tissue interface between the applicator roll and emboss roll mayinvolve the most important transfer of glue, and the shear rate becomesan important consideration for non-Newtonian fluids. If the shear rateis low, the alternative glues will have higher viscosity than 3% PVOH.If the shear rate is above about 10 sec⁻¹, the alternative glues will bethinner. Given that the roll speeds are matched and the nip pressure islow, the shear rate is expected to be low. Thus, the alternative gluesare hypothesized to act as higher viscosity glues in terms of wet tackwhile delivering a smaller quantity of dry residual.

Peel Test Plybond

In order to characterize the adhesive strength of each glue, a strip ofTAD basesheet was adhered to a metal plate followed by measurement ofthe force required to peel the sheet off. Ten drops of glueapproximately 0.5 g was evenly spread on a 2″×8″ stainless steel testpanel plate using a number 40 wire rod to apply a film of approximately50 microns, followed by attaching a 2″×12″ TAD towel basesheet, seeTable 3 for specifics to the glued plate surface and pressing it fromone end to another for 3 times using a metal roller. After drying theglued towel basesheet, the plybond between basesheet and steel plate wasmeasured by a peeling test using an Instron tensile test machine 5966.The free end of the basesheet strip was separated by hand for 2″. Thespecimen was placed in the testing machine by clamping the steel platein the bottom grip and turning up the free end of the basesheet andclamping it in the upper grip. The peeling test was performed bystripping the basesheet from the steel plate approximately at an angleof 180° and a ramp rate of 10″/min for 10″ displacement. At least 6specimens were tested for each glue sample. After each test, the steelplate was washed with DI water and acetone to remove the residual gluebefore the next use. These tests are generally in accordance with testmethod ASTM D 903-98 except for the differences noted.

Plybond

Generally the force needed to separate a ply of a multi-ply sheet orPlybond is measured with a Lab Master Slip and Friction tester availablefrom Testing Machines, Inc. (Islandia, N.Y.) fitted with a sample clampplatform available from Research Dimensions (Neenah, Wis.). A top ply ofthe sample is separated and clamped in a clamp attached to a load celland the average force required to separate the ply from another ply isrecorded as the plies are separated. Details appear below for 2-plytesting; while 3-ply testing is substantially the same.

Plybond strengths reported herein are determined from the average loadrequired to separate the plies of two-ply tissue, towel, napkin, andfacial finished products using TMI Plybond Lab Master Slip & Frictiontester Model 32-90, with high-sensitivity load measuring option andcustom planar top without elevator available from: Testing Machines Inc.2910 Expressway Drive South Islandia, N.Y. 11722; (800)-678-3221;www.testingmachines.com. Plybond clamps are available from: ResearchDimensions, 1720 Oakridge Road, Neenah, Wis. 54956, Contact:920-722-2289 and Fax: 920-725-6874.

Samples are preconditioned according to TAPPI standards and handled onlyby the edges and corners care being exercised to minimize touching thearea of the sample to be tested.

At least ten sheets following the tail seal are discarded. Four samplesare cut from the roll thereafter, each having a length equivalent to 2sheets but the cuts are made ¼″ away from the perf lines by making afirst CD cut ¼″ before a first perforation and a second CD cut ¼″ beforethe third perforation so that the second perforation remains roughlycentered in the sheet. The plies of the each specimen are initiallyseparated in the leading edge area before the first perforationcontinuing to approximately ½″ past this perforation.

The sample is positioned so that the interior ply faces upwardly, theseparated portion of the ply is folded back to a location ½″ from theinitial cut and ¼″ from the first perforation, and creased there. Thefolded back portion of the top ply is secured in one clamp so that theline contact of the top grip is on the perforation; and the clamp isplaced back onto the load cell. The exterior ply of the samples issecured to the platform, aligning the perforation with the line contactof the grip and centering it with the clamp edges.

After ensuring that the sample is aligned with the clamps andperforations, the load-measuring arm is slowly moved to the left at aspeed of 25.4 cm/min, the average load on the arm (in g.) is measuredand recorded. The average of 3 samples is recorded with the fourthsample being reserved for use in case of damage to one of the firstthree. See U.S. Pat. No. 8,287,986.

Plybond and Peel Test Plybond values for various glues are shown inFIGS. 2, 6, 7, 10, 11, 20, 21 and 22. It is seen in FIG. 2, inparticular, that NFC greatly increases Peel Test Plybond tested on TADtowel basesheet up to 300% and more, as compared to the same gluecomposition without any NFC. In FIGS. 6, 10, 11 it is seen that Plybondvalues are significantly increased by addition of NFC in relativelysmall amounts.

A comparison of the adhesion between conventional PVOH glues and NFCreinforced PVOH glues are shown in FIG. 20 for Peel Test Plybond testedon TAD towel. At each PVOH content from 4% to 6%, NFC I reinforced PVOHglues showed stronger adhesion than conventional PVOH. The differencesin adhesion values were significant. Selected results also appear inFIGS. 21 and 22.

Glue Absorbency Rate

Without intending to be bound by any particular theory, the unexpectedand advantageous properties in terms of softness and increased plybondrealized in accordance with the invention are believed due, in part, tothe longer absorption times (Glue Absorbency Rates) exhibited by theinventive adhesives on absorbent sheet in the absence of shear stress.The Glue Absorbency Rate is the time, in seconds, taken for the TADtowel basesheet, Table 3 to completely absorb a 0.05 ml droplet oftested glue. The longer time it takes, the more likely it is for glue tocontribute to plybond rather than being wicked into the towel. Thedroplet is disposed on its surface by way of an automated syringe. Thetest specimens are preferably conditioned at 23° C.±1° C. (73.4±1.8° F.)at 50% relative humidity. For each sample, 4 3×3 inch test specimens areprepared. Each specimen is placed in a sample holder such that a highintensity lamp is directed toward the specimen. 0.05 ml of glue isdeposited on the specimen surface and a stop watch is started. When thedroplet is absorbed, as indicated by lack of further reflection of lightfrom the drop, the stopwatch is stopped and the time recorded to thenearest 0.1 seconds. The procedure is repeated for each specimen and theresults averaged for the sample. Glue Absorbency Rate is otherwisemeasured in accordance with TAPPI method T-432 cm-99.

FIG. 23 is a plot of Glue Absorbency Rate versus PVOH solids on a TADtowel basesheet for various glues. It is seen that the absorption rateof regular PVOH glue increased with increasing PVOH concentration from4% to 5%, and then leveled off from 5% to 6% PVOH. This trend wascoincident with the changes of plybond. The absorption time dramaticallyincreased with the addition of NFC at addition level from 5% to 20%; asmore NFC was added, the longer the absorption time. This result isconsistent with the notion that the reinforcement function of NFC glueas the presence of NFC not only contributes to the hydrogen bonding withthe paper, it also largely restricts the penetration of liquid glue intothe basesheet, allowing the majority of glue to stay as a glue film fordeveloping plybond rather than being wicked by the basesheet. In thisway, it is possible to avoid excessive application of plybond glue whichstiffens the basesheet and reduces the softness of the product.

Embodiments of the Invention

There is thus provided in accordance with the invention in one aspect,embodiment No. 1 which is directed to a multi-ply absorbent sheetcomprising:

-   -   (a) a first absorbent ply of cellulosic sheet;    -   (b) a second absorbent ply of cellulosic sheet; and    -   (c) a ply bonding adhesive interposed between said first        absorbent ply and said second absorbent ply, said ply-bonding        adhesive adhering said absorbent plies together,    -   wherein said ply-bonding adhesive comprises polyvinyl alcohol        and nanofibrillated cellulose.

Embodiment No. 2 is the multi-ply absorbent sheet according toEmbodiment No. 1, wherein said nanofibrillated cellulose has aCharacteristic Breaking Length of at least 3 km.

Embodiment No. 3 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated cellulose has aCharacteristic Breaking Length of from 3 km to 10 km.

Embodiment No. 4 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated cellulose has aCharacteristic Breaking Length of from 4.5 km to 9 km.

Embodiment No. 5 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated cellulose has aCharacteristic Breaking Length of from 6.5 km to 7.5 km.

Embodiment No. 6 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated cellulose has aCharacteristic Nanofiber Viscosity of greater than 200,000 cP at a shearrate of 1 sec⁻¹ and a Characteristic Nanofiber Viscosity of less than50,000 cP at a shear rate of 50 sec⁻¹.

Embodiment No. 7 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated cellulose has aCharacteristic Nanofiber Viscosity of greater than 350 cP at a shearrate of 1 sec⁻¹ and a Characteristic Nanofiber Viscosity of less than 50cP at a shear rate of 50 sec⁻¹.

Embodiment No. 8 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated cellulose has aCharacteristic Nanofiber Viscosity of greater than 4,000 cP at a shearrate of 1 sec⁻¹ and a Characteristic Nanofiber Viscosity of less than1,500 cP at a shear rate of 50 sec⁻¹.

Embodiment No. 9 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 50%as the shear rate is increased from 1 sec⁻¹ to 50 sec⁻¹.

Embodiment No. 10 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 60%as the shear rate is increased from 1 sec⁻¹ to 50 sec⁻¹.

Embodiment No. 11 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 70%as the shear rate is increased from 1 sec⁻¹ to 50 sec⁻¹.

Embodiment No. 12 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated cellulose has aCharacteristic Nanofiber Viscosity of greater than 15,000 cP at a shearrate of 5 sec⁻¹ and a Characteristic Nanofiber Viscosity of less than2,000 cP at a shear rate of 500 sec⁻¹.

Embodiment No. 13 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 60%as the shear rate is increased from 5 sec⁻¹ to 500 sec⁻¹.

Embodiment No. 14 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 70%as the shear rate is increased from 5 sec⁻¹ to 500 sec⁻¹.

Embodiment No. 15 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 80%as the shear rate is increased from 5 sec⁻¹ to 500 sec⁻¹.

Embodiment No. 16 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 90%as the shear rate is increased from 5 sec⁻¹ to 500 sec⁻¹.

Embodiment No. 17 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the polyvinyl alcohol in theadhesives comprises partially hydrolyzed polyvinyl alcohol having adegree of hydrolysis between 70 and 98 mol %.

Embodiment No. 18 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the polyvinyl alcohol in the adhesivehas a Characteristic PVOH Viscosity of from 3 to 75 cP.

Embodiment No. 19 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the polyvinyl alcohol in the adhesivehas a Characteristic PVOH Viscosity of from 25 cP to 55 cP.

Embodiment No. 20 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the adhesive contains from 0.5% byweight to 20% or 30% or 40% or up to 50% by weight of nanofibrillatedcellulose, based on the weight of polyvinyl alcohol.

Embodiment No. 21 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the adhesive contains from 1% byweight to 10% or 20% by weight of nanofibrillated cellulose, based onthe weight of polyvinyl alcohol.

Embodiment No. 22 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the adhesive contains from 1.5% byweight to 5% by weight of nanofibrillated cellulose, based on the weightof polyvinyl alcohol.

Embodiment No. 23 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the adhesive contains from 1.75% byweight to 2.5% by weight of nanofibrillated cellulose, based on theweight of polyvinyl alcohol.

Embodiment No. 24 is the multi-ply tissue sheet according to any of theforegoing embodiments, wherein the adhesive is applied between the pliesas an aqueous composition containing from 1.5% to 10% by weight of thecomposition polyvinyl alcohol.

Embodiment No. 25 is the multi-ply tissue sheet according to any of theforegoing embodiments, wherein the adhesive is applied between the pliesas an aqueous composition containing from 1.5% to 6% by weight of thecomposition polyvinyl alcohol.

Embodiment No. 26 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the adhesive is applied between theplies as an aqueous composition containing from 1.5% to 3% by weight ofthe composition polyvinyl alcohol.

Embodiment No. 27 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the adhesive is applied between theplies in a discontinuous pattern.

Embodiment No. 28 is the multi-ply absorbent sheet according toEmbodiment No. 27, wherein the discontinuous pattern corresponds to apattern of raised embossments on one of the absorbent plies ofcellulosic sheet.

Embodiment No. 29 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the multi-ply absorbent sheet is amulti-ply tissue sheet composed predominantly of hardwood papermakingfiber.

Embodiment No. 30 is the multi-ply tissue sheet according to EmbodimentNo. 29, wherein the adhesive is applied between the plies as an aqueouscomposition containing from 1.5% to 7.5% by weight of the compositionpolyvinyl alcohol and the adhesive comprises from 1.5% to 10% by weightnanofibrillated fiber based on the weight of polyvinyl alcohol.

Embodiment No. 31 is the multi-ply tissue sheet according to EmbodimentNo. 29, wherein the adhesive is applied between the plies as an aqueouscomposition containing from 1.5% to 3% by weight of the compositionpolyvinyl alcohol and the adhesive comprises from 1.5% to 10% by weightnanofibrillated fiber based on the weight of polyvinyl alcohol.

Embodiment No. 32 is the multi-ply tissue sheet according to EmbodimentNo. 29, having a basis weight of 20 to 40 lbs/3000 ft².

Embodiment No. 33 is the multi-ply absorbent sheet according to any oneof Embodiment Nos. 1 through 28, wherein the multi-ply absorbent sheetis a multi-ply towel sheet composed predominantly of softwood fiber.

Embodiment No. 34 is the multi-ply towel sheet according to EmbodimentNo. 33, having a basis weight of from 20 to 40 lbs/3000 ft².

Embodiment No. 35 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, wherein the multi-ply sheet comprises a thirdabsorbent ply of cellulosic sheet plied together with the first andsecond ply.

Embodiment No. 36 is the multiply absorbent sheet according to any ofthe foregoing embodiments, consisting of three plies laminated together,wherein the ply bonding adhesive is applied only between two plies priorto lamination.

Embodiment No. 37 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, which exhibits a Relative Plybond value of atleast 110% as compared with a like product made without nanofibrillatedcellulose in the adhesive.

Embodiment No. 38 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, which exhibits a Relative Plybond value of atleast 125% as compared with a like product made without nanofibrillatedcellulose in the adhesive.

Embodiment No. 39 is the multi-ply absorbent sheet according to any ofthe foregoing embodiments, which exhibits a Relative Plybond value of atleast 140% as compared with a like product made without nanofibrillatedcellulose in the adhesive.

Embodiment No. 40 is a method of making absorbent sheet comprising:

-   -   (a) feeding a first absorbent cellulosic basesheet to an        embossing nip;    -   (b) embossing a pattern of raised embossments in said first        basesheet;    -   (c) applying an aqueous adhesive containing polyvinyl alcohol        and nanofibrillated cellulose to the raised embossments of said        first sheet; and    -   (d) plying a second absorbent cellulosic basesheet with said        first sheet by pressing said second cellulosic sheet to the        adhesive disposed on the raised embossments of said first        cellulosic sheet.

Embodiment No. 41 is the method of making a multi-ply absorbent sheetaccording to Embodiment No. 40, wherein said nanofibrillated cellulosehas a Characteristic Breaking Length of at least 3 km.

Embodiment No. 42 is the method of making a multi-ply absorbent sheetaccording to Embodiment Nos. 40 or 41, wherein said nanofibrillatedcellulose has a Characteristic Breaking Length of from 3 km to 10 km.

Embodiment No. 43 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiment Nos. 40 through 42, wherein saidnanofibrillated cellulose has a Characteristic Breaking Length of from4.5 km to 9 km.

Embodiment No. 44 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiment Nos. 40 through 43, wherein saidnanofibrillated cellulose has a Characteristic Breaking Length of from6.5 km to 7.5 km.

Embodiment No. 45 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiment Nos. 40 through 44 wherein saidnanofibrillated cellulose has a Characteristic Nanofiber Viscosity ofgreater than 200,000 cP at a shear rate of 1 sec⁻¹ and a CharacteristicNanofiber Viscosity of less than 50,000 cP at a shear rate of 50 sec⁻¹.

Embodiment No. 46 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiment Nos. 40 through 45, wherein saidnanofibrillated cellulose has a Characteristic Nanofiber Viscosity ofgreater than 350 cP at a shear rate of 1 sec⁻¹ and a CharacteristicNanofiber Viscosity of less than 50 cP at a shear rate of 50 sec⁻¹.

Embodiment No. 47 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiment Nos. 40 through 46, wherein saidnanofibrillated cellulose has a Characteristic Nanofiber Viscosity ofgreater than 4,000 cP at a shear rate of 1 sec⁻¹ and a CharacteristicViscosity of less than 1,500 cP at a shear rate of 50 sec⁻¹.

Embodiment No. 48 is the method of making a multi-ply absorbed sheetaccording to any one of Embodiment Nos. 40 through 47, wherein saidnanofibrillated cellulose exhibits a Characteristic Nanofiber Viscosityreduction of at least 50% as the shear rate is increased from 1 sec⁻¹ to50 sec⁻¹.

Embodiment No. 49 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiment Nos. 40 through 48, wherein saidnanofibrillated cellulose exhibits a Characteristic Nanofiber Viscosityreduction of at least 60% as the shear rate is increased from 1 sec⁻¹ to50 sec⁻¹.

Embodiment No. 50 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiment Nos. 40 through 49, wherein saidnanofibrillated cellulose exhibits a Characteristic Nanofiber Viscosityreduction of at least 70% as the shear rate is increased from 1 sec⁻¹ to50 sec⁻¹.

Embodiment No. 51 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 50, wherein saidnanofibrillated cellulose has a Characteristic Nanofiber Viscosity ofgreater than 15,000 cP at a shear rate of 5 sec⁻¹ and a CharacteristicNanofiber Viscosity of less than 2,000 cP at a shear rate of 500 sec⁻¹.

Embodiment No. 52 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 51, wherein saidnanofibrillated cellulose exhibits a Characteristic Nanofiber Viscosityreduction of at least 60% as the shear rate is increased from 5 sec⁻¹ to500 sec⁻¹.

Embodiment No. 53 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 52, wherein saidnanofibrillated cellulose exhibits a Characteristic Nanofiber Viscosityreduction of at least 70% as the shear rate is increased from 5 sec⁻¹ to500 sec⁻¹.

Embodiment No. 54 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 53, wherein saidnanofibrillated cellulose exhibits a Characteristic Nanofiber Viscosityreduction of at least 80% as the shear rate is increased from 5 sec⁻¹ to500 sec⁻¹.

Embodiment No. 55 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 54, wherein saidnanofibrillated cellulose exhibits a Characteristic Nanofiber Viscosityreduction of at least 90% as the shear rate is increased from 5 sec⁻¹ to500 sec⁻¹.

Embodiment No. 56 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 55, wherein thepolyvinyl alcohol in the adhesives comprises partially hydrolyzedpolyvinyl alcohol having a degree of hydrolysis between 70 and 98 mol %.

Embodiment No. 57 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 56, wherein thepolyvinyl alcohol in the adhesive has a Characteristic PVOH Viscosity offrom 3 to 75 cP.

Embodiment No. 58 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 57, wherein thepolyvinyl alcohol in the adhesive has a Characteristic PVOH Viscosity offrom 25 cP to 55 cP.

Embodiment No. 59 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 58, wherein theadhesive contains from 0.5% by weight to 20% or 30% or 40% or up to 50%by weight of nanofibrillated cellulose, based on the weight of polyvinylalcohol.

Embodiment No. 60 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 59, wherein theadhesive contains from 1% by weight to 10% by weight of nanofibrillatedcellulose, based on the weight of polyvinyl alcohol.

Embodiment No. 61 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 60, wherein theadhesive contains from 1.5% by weight to 5% by weight of nanofibrillatedcellulose, based on the weight of polyvinyl alcohol.

Embodiment No. 62 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 61, wherein theadhesive contains from 1.75% by weight to 2.5% by weight ofnanofibrillated cellulose, based on the weight of polyvinyl alcohol.

Embodiment No. 63 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 62, wherein theadhesive is applied between the plies as an aqueous solution containingfrom 1.5% to 10% by weight of the composition polyvinyl alcohol.

Embodiment No. 64 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 63, wherein theadhesive is applied between the plies as an aqueous solution containingfrom 1.5% to 6% by weight of the composition polyvinyl alcohol.

Embodiment No. 65 is the method of making a multi-ply absorbent sheetaccording to any one of Embodiments Nos. 40 through 64, wherein theadhesive is applied between the plies as an aqueous solution containingfrom 1.5% to 3% by weight of the composition polyvinyl alcohol.

Embodiment No. 66 is the method of making a multi-ply absorbent sheetaccording to any of Embodiment Nos. 40 through 65, further comprisingplying a third cellulosic basesheet with said first and secondcellulosic basesheets without additional adhesive.

Embodiment No. 67 is a ply bonding adhesive for the manufacture ofmulti-ply paper tissue and multi-ply paper towel comprising:

-   -   (a) water;    -   (b) polyvinyl alcohol in an amount of from 1.5% to 10% by weight        based on the weight of the adhesive composition; and    -   (c) from 1% to 50% by weight of nanofibrillated cellulose based        on the weight of polyvinyl alcohol in the adhesive.

Embodiment No. 68 is the ply bonding adhesive according to EmbodimentNo. 67, wherein said nanofibrillated cellulose has a CharacteristicBreaking Length of at least 3 km.

Embodiment No. 69 is the ply bonding adhesive according to EmbodimentNos. 67 or 68, wherein said nanofibrillated cellulose has aCharacteristic Breaking Length of from 3 km to 10 km.

Embodiment No. 70 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 69, wherein said nanofibrillated cellulosehas a Characteristic Breaking Length of from 4.5 km to 9 km.

Embodiment No. 71 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 70, wherein said nanofibrillated cellulosehas a Characteristic Breaking Length of from 6.5 km to 7.5 km.

Embodiment No. 72 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 71, wherein said nanofibrillated cellulosehas a Characteristic Nanofiber Viscosity of greater than 200,000 cP at ashear rate of 1 sec⁻¹ and a Characteristic Nanofiber Viscosity of lessthan 50,000 cP at a shear rate of 50 sec⁻¹.

Embodiment No. 73 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 72, wherein said nanofibrillated cellulosehas a Characteristic Nanofiber Viscosity of greater than 350 cP at ashear rate of 1 sec⁻¹ and a Characteristic Nanofiber Viscosity of lessthan 50 cP at a shear rate of 50 sec⁻¹.

Embodiment No. 74 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 73, wherein said nanofibrillated cellulosehas a Characteristic Nanofiber Viscosity of greater than 4,000 cP at ashear rate of 1 sec⁻¹ and a Characteristic Nanofiber Viscosity of lessthan 1,500 cP at a shear rate of 50 sec⁻¹.

Embodiment No. 75 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 74, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 50%as the shear rate is increased from 1 sec⁻¹ to 50 sec⁻¹.

Embodiment No. 76 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 75, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 60%as the shear rate is increased from 1 sec⁻¹ to 50 sec⁻¹.

Embodiment No. 77 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 76, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 70%as the shear rate is increased from 1 sec⁻¹ to 50 sec⁻¹.

Embodiment No. 78 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 77, wherein said nanofibrillated cellulosehas a Characteristic Nanofiber Viscosity of greater than 15,000 cP at ashear rate of 5 sec⁻¹ and a Characteristic Nanofiber Viscosity of lessthan 2,000 cP at a shear rate of 500 sec⁻¹.

Embodiment No. 79 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 78, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 60%as the shear rate is increased from 5 sec⁻¹ to 500 sec⁻¹.

Embodiment No. 80 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 79, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 70%as the shear rate is increased from 5 sec⁻¹ to 500 sec⁻¹.

Embodiment No. 81 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 80, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 80%as the shear rate is increased from 5 sec⁻¹ to 500 sec⁻¹.

Embodiment No. 82 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 81, wherein said nanofibrillated celluloseexhibits a Characteristic Nanofiber Viscosity reduction of at least 90%as the shear rate is increased from 5 sec⁻¹ to 500 sec⁻¹.

Embodiment No. 83 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 82, wherein the polyvinyl alcohol in theadhesives comprises partially hydrolyzed polyvinyl alcohol having adegree of hydrolysis between 70 and 98 mol %.

Embodiment No. 84 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 83, wherein the polyvinyl alcohol in theadhesive has a Characteristic PVOH Viscosity of from 3 to 75 cP.

Embodiment No. 85 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 84, wherein the polyvinyl alcohol in theadhesive has a Characteristic PVOH Viscosity of from 25 cP to 55 cP.

Embodiment No. 86 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 85, wherein the adhesive contains from 0.5%by weight to 20% or 30% or 40% or up to 50% by weight of nanofibrillatedcellulose, based on the weight of polyvinyl alcohol.

Embodiment No. 87 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 86, wherein the adhesive contains from 1% byweight to 10% by weight of nanofibrillated cellulose, based on theweight of polyvinyl alcohol.

Embodiment No. 88 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 87, wherein the adhesive contains from 1.5%by weight to 5% by weight of nanofibrillated cellulose, based on theweight of polyvinyl alcohol.

Embodiment No. 89 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 88, wherein the adhesive contains from 1.75%by weight to 2.5% by weight of nanofibrillated cellulose, based on theweight of polyvinyl alcohol.

Embodiment No. 90 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 89, wherein the adhesive is applied betweenplies of a multi-ply absorbent sheet as an aqueous compositioncontaining from 1.5% to 10% by weight of the composition polyvinylalcohol.

Embodiment No. 91 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 90, wherein the adhesive is applied betweenplies of a multi-ply absorbent sheet as an aqueous compositioncontaining from 1.5% to 6% by weight of the composition polyvinylalcohol.

Embodiment No. 92 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 91, wherein the adhesive is applied betweenplies of a multi-ply absorbent sheet as an aqueous compositioncontaining from 1.5% to 3% by weight of the composition polyvinylalcohol.

Embodiment No. 93 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 92, wherein the adhesive comprises from90-98.5% by weight of the composition water, from to 1.5% to 6% byweight of the composition polyvinyl alcohol and from 1% to 20% or 30% or40% or up to 50% by weight of nanofibrillated cellulose based on theweight of polyvinyl alcohol in the adhesive.

Embodiment No. 94 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 93, wherein the adhesive comprises from94-98.5% by weight of the composition water, from to 1.5% to 6% byweight of the composition polyvinyl alcohol and from 1% to 20% or 30% or40% or up to 50% by weight of nanofibrillated cellulose based on theweight of polyvinyl alcohol in the adhesive.

Embodiment No. 95 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 94, wherein the adhesive comprises from97-98.5% by weight of the composition water, from to 1.5% to 2.5% byweight of the composition polyvinyl alcohol and from 1% to 5% by weightof nanofibrillated cellulose based on the weight of polyvinyl alcohol inthe adhesive.

Embodiment No. 96 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 94, wherein the adhesive comprises from94-98.5% by weight of the composition water, from to 1.5% to 6% byweight of the composition polyvinyl alcohol and from 1% to 20% by weightof nanofibrillated cellulose based on the weight of polyvinyl alcohol inthe adhesive.

Embodiment No. 97 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 96, wherein the adhesive consists essentiallyof water, polyvinyl alcohol and nanofibrillated cellulose.

Embodiment No. 98 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 97, wherein the adhesive exhibits an AdhesiveViscosity reduction of at least 15% as shear rate is increased from 1sec⁻¹ to 100 sec⁻¹.

Embodiment No. 99 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 98, wherein the adhesive exhibits an AdhesiveViscosity reduction of at least 25% as shear rate is increased from 1sec⁻¹ to 100 sec⁻¹.

Embodiment No. 100 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 99, wherein the adhesive exhibits an AdhesiveViscosity reduction of at least 50% as shear rate is increased from 1sec⁻¹ to 100 sec⁻¹.

Embodiment No. 101 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 100, wherein the adhesive exhibits a RelativePeel Test Plybond value of at least 115% as compared to an adhesive ofthe same composition without nanofibrillated cellulose.

Embodiment No. 102 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 101, wherein the adhesive exhibits a RelativePeel Test Plybond value of at least 125% as compared to an adhesive ofthe same composition without nanofibrillated cellulose.

Embodiment No. 103 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 102, wherein the adhesive exhibits a RelativePeel Test Plybond value of at least 150% as compared to an adhesive ofthe same composition without nanofibrillated cellulose.

Embodiment No. 104 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 103, wherein the adhesive exhibits a RelativePeel Test Plybond value of at least 200% as compared to an adhesive ofthe same composition without nanofibrillated cellulose.

Embodiment No. 105 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 104, wherein the adhesive exhibits a RelativePeel Test Plybond value of at least 250% as compared to an adhesive ofthe same composition without nanofibrillated cellulose.

Embodiment No. 106 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 105, wherein the adhesive exhibits a RelativePeel Test Plybond value of at least 300% as compared to an adhesive ofthe same composition without nanofibrillated cellulose.

Embodiment No. 107 is the ply bonding adhesive according to any one ofEmbodiment Nos. 67 through 106, wherein the adhesive exhibits a RelativePeel Test Plybond value of at least 400% as compared to an adhesive ofthe same composition without nanofibrillated cellulose.

Embodiment No. 108 is a ply bonding adhesive composition for themanufacture of multi-ply paper tissue and multi-ply paper towelcomprising: (a) water; (b) polyvinyl alcohol; and (c) nanofibrillatedcellulose.

Embodiment no. 109 is the ply bonding adhesive composition according toEmbodiment No. 108, wherein the adhesive comprises from 90-98.5% byweight of the composition water, from to 0.5% to 10% by weight of thecomposition polyvinyl alcohol and from 0.05% to 2.5% by weight of thecomposition nanofibrillated cellulose.

Embodiment No. 110 is the ply bonding adhesive composition according toEmbodiment Nos. 108 or 109, wherein the weight ratio of nanofibrillatedcellulose:PVOH is greater than 0.025 and up to 2.

Embodiment No. 111 is the ply bonding adhesive composition according toEmbodiment Nos. 108 to 110, wherein the weight ratio of nanofibrillatedcellulose:PVOH is greater than 0.25 and up to 2.

Embodiment No. 112 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 110, wherein the weight ratio ofnanofibrillated cellulose:PVOH is greater than 0.2.

Embodiment No. 113 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 112, wherein the weight ratio ofnanofibrillated cellulose:PVOH is greater than 0.3

Embodiment No. 114 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 113, wherein the weight ratio ofnanofibrillated cellulose:PVOH is greater than 0.4.

Embodiment No. 115 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 114, wherein the weight ratio ofnanofibrillated cellulose:PVOH is greater than 0.5.

Embodiment No. 116 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 115, wherein the weight ratio ofnanofibrillated cellulose:PVOH is greater than 0.6.

Embodiment No. 117 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 110, wherein the weight ratio ofnanofibrillated cellulose:PVOH is greater than 0.2 and up to 2.

Embodiment No. 118 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 117, wherein nanofibrillated cellulose ispresent in an amount of greater than 0.4 percent by weight based on theweight of the aqueous composition.

Embodiment No. 119 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 118, wherein nanofibrillated cellulose ispresent in an amount of greater than 0.4 percent by weight based on theweight of the aqueous composition and up to 1.5 percent by weight basedon the weight of the aqueous composition.

Embodiment No. 120 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 119, wherein the ply bonding adhesivecontains from 0.25 percent by weight to 3 percent by weight ofnanofibrillated cellulose based on the weight of the aqueouscomposition.

Embodiment No. 121 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 120, wherein the ply bonding adhesivecontains from 0.25 percent by weight to 2.5 percent by weight ofnanofibrillated cellulose based on the weight of the aqueouscomposition.

Embodiment No. 122 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 121, wherein the ply bonding adhesivecontains from 0.35 percent by weight to 1.5 percent by weight ofnanofibrillated cellulose based on the weight of the aqueouscomposition.

Embodiment No. 123 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 122, wherein the ply bonding adhesivecontains from 0.35 percent by weight to 1 percent by weight ofnanofibrillated cellulose based on the weight of the aqueouscomposition.

Embodiment No. 124 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 123, wherein the ply bonding adhesivecontains from 0.35 percent by weight to 0.75 percent by weight ofnanofibrillated cellulose based on the weight of the aqueouscomposition.

Embodiment No. 125 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 124, wherein the ply bonding adhesivecontains from 0.4 percent by weight to 0.6 percent by weight ofnanofibrillated cellulose based on the weight of the aqueouscomposition.

Embodiment no. 126 is the ply bonding adhesive composition according toany of Embodiment Nos. 108 to 125, wherein the adhesive comprises from90-98.5% by weight of the composition water, from to 0.5% to 10% byweight of the composition polyvinyl alcohol and from 0.25% to 2.5% byweight of the composition nanofibrillated cellulose.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. Such modifications are also to be considered aspart of the present invention. In view of the foregoing discussion,relevant knowledge in the art and references discussed above inconnection with the Background of the Invention, the disclosures ofwhich are all incorporated herein by reference, further description isdeemed unnecessary. In addition, it should be understood from theforegoing discussion that aspects of the invention and portions ofvarious embodiments may be combined or interchanged either in whole orin part. Furthermore, those of ordinary skill in the art will appreciatethat the foregoing description is by way of example only, and is notintended to limit the invention.

What is claimed is:
 1. A method of making absorbent sheet comprising:(a) feeding a first absorbent cellulosic basesheet to an embossing nip;(b) embossing a pattern of raised embossments in said first basesheet;(c) applying an aqueous adhesive containing polyvinyl alcohol andnanofibrillated cellulose to the raised embossments of said first sheet;and (d) plying a second absorbent cellulosic basesheet with said firstsheet by pressing said second cellulosic sheet to the adhesive disposedon the raised embossments of said first cellulosic sheet, wherein theaqueous adhesive containing polyvinyl alcohol and nanofibrillatedcellulose comprises (a) water; (b) polyvinyl alcohol in an amount offrom 1.5% to 10% by weight based on the weight of the adhesivecomposition; and (c) from 1% to 50% by weight of nanofibrillatedcellulose based on the weight of polyvinyl alcohol in the adhesive. 2.The method of making a multi-ply absorbent sheet according to claim 1,wherein said nanofibrillated cellulose exhibits a CharacteristicNanofiber Viscosity reduction of at least 80% as the shear rate isincreased from 5 sec¹ to 500 sec⁻¹.
 3. The method of making a multi-plyabsorbent sheet according to claim 1, wherein said nanofibrillatedcellulose has a Characteristic Breaking Length of at least 3 km.
 4. Themethod of making a multi-ply absorbent sheet according to claim 3,wherein said nanofibrillated cellulose has a Characteristic BreakingLength of from 3 km to 10 km.
 5. The method of making a multi-plyabsorbent sheet according to claim 4, wherein said nanofibrillatedcellulose has a Characteristic Breaking Length of from 4.5 km to 9 km.6. The method of making a multi-ply absorbent sheet according to claim5, wherein said nanofibrillated cellulose has a Characteristic BreakingLength of from 6.5 km to 7.5 km.
 7. The method of making a multi-plyabsorbent sheet according to claim 1, wherein the polyvinyl alcohol inthe adhesive comprises partially hydrolyzed polyvinyl alcohol having adegree of hydrolysis between 70 and 98 mol %.
 8. The method of making amulti-ply absorbent sheet according to claim 1, wherein the adhesivecontains from 1.5% by weight to 5% by weight of nanofibrillatedcellulose, based on the weight of polyvinyl alcohol.
 9. The method ofmaking a multi-ply absorbent sheet according to claim 1, wherein theadhesive contains from 1.75% by weight to 2.5% by weight ofnanofibrillated cellulose, based on the weight of polyvinyl alcohol. 10.The method of making a multi-ply absorbent sheet according to claim 1,wherein the adhesive is applied between the plies as an aqueous solutioncontaining from 1.5% to 10% by weight of the composition polyvinylalcohol.
 11. The method of making a multi-ply absorbent sheet accordingto claim 10, wherein the adhesive is applied between the plies as anaqueous solution containing from 1.5% to 6% by weight of the compositionpolyvinyl alcohol.
 12. The method of making a multi-ply absorbent sheetaccording to claim 10, wherein the adhesive is applied between the pliesas an aqueous solution containing from 1.5% to 3% by weight of thecomposition polyvinyl alcohol.
 13. A ply bonding adhesive for themanufacture of multi-ply paper tissue and multi-ply paper towelcomprising: (a) water; (b) polyvinyl alcohol in an amount of from 1.5%to 10% by weight based on the weight of the adhesive composition; and(c) from 1% to 50% by weight of nanofibrillated cellulose based on theweight of polyvinyl alcohol in the adhesive.
 14. The ply bondingadhesive according to claim 13, wherein the adhesive comprises from90-98.5% by weight of the composition water, from to 1.5% to 6% byweight of the composition polyvinyl alcohol and from 1% to 30% by weightof nanofibrillated cellulose based on the weight of polyvinyl alcohol inthe adhesive.
 15. The ply bonding adhesive according to claim 13,wherein the adhesive comprises from 94-98.5% by weight of thecomposition water, from to 1.5% to 6% by weight of the compositionpolyvinyl alcohol and from 1% to 30% by weight of nanofibrillatedcellulose based on the weight of polyvinyl alcohol in the adhesive. 16.A ply bonding adhesive composition for the manufacture of multi-plypaper tissue and multi-ply paper towel comprising: (a) water; (b)polyvinyl alcohol; and (c) nanofibrillated cellulose, wherein theadhesive comprises from 90-98.5% by weight of the composition water, atleast 0.5% by weight of the composition polyvinyl alcohol and from 0.05%to 2.5% by weight of the composition nanofibrillated cellulose.
 17. Theply bonding adhesive composition according to claim 16, wherein theweight ratio of nanofibrillated cellulose:PVOH is greater than 0.025 andup to
 2. 18. The ply bonding adhesive composition according to claim 17,wherein the weight ratio of nanofibrillated cellulose:PVOH is greaterthan 0.25 and up to
 2. 19. The ply bonding adhesive compositionaccording to claim 17, wherein nanofibrillated cellulose is present inan amount of greater than 0.4 percent by weight based on the weight ofthe aqueous composition and up to 1.5 percent by weight based on theweight of the aqueous composition.
 20. The ply bonding adhesivecomposition according to claim 16, wherein said nanofibrillatedcellulose has a Characteristic Breaking Length of from 3 km to 10 km.